Sebum, or skin oil, is produced in the sebaceous glands located in the pilosebaceous apparatus of the skin and reaches the skin surface through the duct of the hair follicles. The presence of excessive amounts of sebum on the skin surface often results in an unattractive cosmetic condition commonly known as "oily skin". Sebum also plays an important role in the pathogenesis of acne. Sebaceous gland activity is significantly increased in acne subjects, and individuals with the most severe acne often have the highest sebum secretion rates.
The spreading of sebum on the skin surface is thus an important cosmetic parameter since its distribution on the skin surface can determine the appearance of oiliness or greasiness and can contribute to the severity of acne.
It is advantageous, therefore, to have available means for controlling the distribution of sebum over the surface of human skin, with particular regard to skin characterized by an excessive secretion or presence of sebum upon the surface and to affected skin areas of, for example, acne patients.
Currently marketed leave-on facial emulsion products do not effectively control the distribution of sebum upon the surface of the skin. Without being limited by theory, it is believed that current leave-on emulsion products undesirably modify the surface properties of the skin, thereby increasing the contact angle of the sebum with the skin and thus preventing its spreading. These products cause the secreted sebum to remain as small discreet droplets upon the skin, thus resulting in oily skin and its attendant problems.
Typically, the problem of oily facial skin has been dealt with by frequent cleansing and the use of astringent preparations. However, such remedies are of questionable efficacy and not always practical, and also have the disadvantage of drying, irritating, and abrading the skin. Additionally, any benefits which may be obtained through cleansing and the use of astringents are only temporary. Once the skin has been cleansed of sebum, the skin begins secreting sebum anew so that the oily skin problem soon returns.
The prior art teaches the incorporation of clays, talcs, silicas, starches, polymers, and other such materials into skin care products for absorbing sebum and controlling oily skin. See U.S. Pat. No. 4,940,578, Yoshihara, T. et al., issued July 10, 1990; U.S. Patent 4,885,109, to Umemoto, I. et al., issued Dec. 5, 1989; U.S. Pat. No. 4,536,399, to Flynn, R. G. et al., issued Aug. 20, 1985; U.S. Pat. No. 4,489,058, to Lay, G. E. et al., issued Dec. 18, 1984; U.S. Pat. No. 4,388,301, to Klein, R. W., issued June 14, 1983; and U.S. Pat. No. 4,000,317, to Menda, W. C. et al., issued Dec. 28, 1976. However, the practicality of incorporating sebum absorbing materials is limited by the sebum absorbing capacity of the material, formulation difficulties, and the negative aesthetic properties which these materials impart to finished products. Also, any oil control benefit which may be obtained is merely temporary.
A longer lasting method of reducing sebum on the skin is through the use of topical or systemic agents believed to provide a sebosuppressive effect. See Karg, G. et al., "Sebosuppression", Cosmetics & Toiletries. vol. 102, pp. 140-146 (April 1987); U.S. Pat. No. 4,593,021, to Hsia, S. L. et al., issued June 3, 1986; U.S. Pat. No. 4,587,235, to Bittler, D. et al., issued May 6, 1986; U.S. Pat. No. 4,529,587, to Green, M. R., issued July 16, 1985; ; U.S. Pat. No. 4,210,654 to Bauer et al., issued July 1, 1980; and U.S. Pat. No. 4,016,287, to Eberhardt et al., issued Apr. 5, 1977. Without being limited by theory, it is believed that sebosuppressive agents decrease the sebum output of the pilosebaceous ducts of the skin, thereby reducing surface oiliness. However, many sebosuppressive agents are potent drugs having undesirable side effects on diuretic activity, inflammation mediators, blood pressure, hormonal levels, cholesterol synthesis, and other bodily functions. Thus, it may not always be practical, desirable, or even possible to utilize sebosuppressive agents to control oily skin.
The control of sebum spreading via topical formulations which do not contain sebosuppressive agents is described in Australian Patent Application 8,319,558 to Herstein et al., published Apr. 12, 1984. This patent discloses formulations for use on oily skin such as cleansers, shampoos, and anti-acne treatments, which contain y-gluconamidopropyl dimethyl 2-hydroxyethyl ammonium chloride. However, these formulations have the undesirable characteristic of increasing the contact angle of sebum with the skin and inhibiting the even spreading and distribution of the sebum. Also, none of the formulations disclosed are leave-on emulsion type lotions or creams.
Furthermore, in addition to the limitations of the prior art discussed above, most currently marketed emulsion products actually contribute to and aggravate oily skin problems. Most emulsion products are oil-in-water or water-in-oil emulsions containing high levels of fats and oils. The high levels of fats and oils in these products give them their characteristic heavy and greasy aesthetics and contribute to oily skin problems. The limited number of products which claim to be free from fats and oils are usually not emulsion type products, but instead are low viscosity, hydro-alcoholic formulations which are too harsh and astringent for regular or frequent use.
Other cosmetic compositions are disclosed in, for example U.S. Pat. No. 4,387,019 to Georgalas et al., issued June 16, 1989 and also in U.S. Pat. No. 4,863,725 to Deckner et al., issued Sept. 5, 1989, both of which are incorporated by reference herein.
Therefore, it would be highly desirable to develop leave-on facial emulsion compositions which overcome the disadvantages of the prior art.
It is therefore an object of the present invention to provide leave-on facial emulsion compositions which reduce the oily appearance and greasy feel of facial skin. It is another object of the present invention to provide compositions for controlling the distribution of sebum upon the skin surface. It is still another object of the present invention to provide compositions which are aesthetically pleasing and substantially free from fats and oils. It is yet another object of the present invention to provide compositions for controlling sebum distribution without incorporating oil-absorbing materials. It is a further object of the present invention to provide compositions for controlling sebum distribution without using sebosuppressive drug agents. It is an even further object of the present invention to provide compositions which reduce the contact angle between sebum and skin. It is yet a further object of the present invention to provide compositions which distribute sebum evenly across the surface of the skin. It is another object of the present invention to retard the regreasing of the skin by sebum. It is yet another object of the present invention to provide methods for reducing the oily appearance and greasy feel of facial skin.
These and other objects of this invention will become apparent in light of the following disclosure.